1. Technical Field
The present invention relates in general to data networks, and in particular, to a link aggregation group (LAG) for a Layer 2 data network, such as a Transparent Interconnection of Lots of Links (TRILL) network.
2. Description of the Related Art
The IEEE 802.1D standard defines the Spanning Tree Protocol (STP), which is a conventional data link layer protocol that ensures that a bridged Ethernet network is free of bridge loops and that a single active network path exists between any given pair of network nodes. Current trends for packet-switched data networks—including the convergence of local area network (LAN) and storage area network (SAN) traffic (e.g., Fibre Channel, Fibre Channel over Ethernet (FCoE), Internet Small Computer System Interface (iSCSI), etc.), rapidly increasing bandwidth capacities of (and demand on) network links, and increased virtualization of network resources and infrastructure—place significant additional demands on network infrastructure and management.
These demands have exposed weaknesses in STP and have generated significant industry interest in replacing STP with a more robust, efficient, and flexible Layer 2 protocol. For example, because STP permits only a single active network path between any two network nodes and blocks all alternate network paths, aggregate network bandwidth is artificially reduced and is inefficiently utilized. STP also reacts to even small topology changes and may force partitioning of virtual LANs due to network connectivity changes. In addition, the Ethernet header of STP frames does not include a hop count (or Time to Live (TTL)) field, limiting flexibility. Furthermore, because only a single active network link is supported between any two nodes, STP has poor fault tolerance, lengthy failure recovery (which can require broadcast traffic to relearn forwarding paths) and low reliability (i.e., dropped traffic).
In view of the weaknesses of STP, the Internet Engineering Task Force (IETF) has recently proposed to replace STP with a new set of Transparent Interconnection of Lots of Links (TRILL) protocols, defined, for example, in Perlman, R., et al., “RBridges: Appointed Forwarders”, Internet-Draft, expires Nov. 18, 2011, and Perlman, R., et al., “RBridges: Base Protocol Specification”, Internet-Draft, expires September 2010, which has been superseded by RFC6325 “RBridges: Base Protocol Specification,” dated July 2011 and incorporated herein by reference. These and other TRILL protocols presuppose the use of IS-IS (as defined, for example, in IETF RFC6165) in the control plane.
With the use of TRILL protocols, regular L2 traffic is tunneled and passed via a special routing methodology (referred to herein as TRILL routing) in a TRILL campus comprising a network of RBridges and links (and possibly intervening standard L2 bridges) bounded by end stations. Multi-pathing is currently supported for unicast and multidestination traffic within a TRILL campus, but not on its boundary. Thus, at run time TRILL permits an external switch or server to have only one active link connected to a TRILL campus for the same Virtual LAN (VLAN).
The present application recognizes that it is desirable to promote high availability by supporting redundant links between external nodes and multiple RBridges in a TRILL campus. The present application additionally recognizes that it is also desirable to place these redundant links into a Link Aggregation Group (LAG) in order to utilize the bandwidth of all the links effectively. Accordingly, the present application discloses mechanisms and associated methodologies, referred to herein as TRILL LAG or t-LAG, that supports connection of external network nodes (e.g., switches and/or servers) to a TRILL campus via a DMLT (Distributed Multi-Link Trunk).